A. Field of the Invention
The present invention relates to a compact photographic color developer concentrate composition comprising a concentrate and a solid component for use in color photographic development of silver halide photographic sensitizing material and a method for processing image-wise exposed silver halide photographic sensitizing materials using the developer concentrate composition.
B. Description of the Related Art
Exposed photographic color silver halide emulsions are generally processed through the steps of color development, de-silvering, washing and stabilization, usually using the following processing solutions: color developer, bleaching solution, fixer, wash water and stabilizing solution. These processing solutions are either prepared from solid chemicals, multi-part liquid concentrates, or diluted, single-part, ready-to-use solutions.
There is a need in the photographic processing industry to reduce the number of multiple liquid concentrates necessary for the preparation of working solutions and replenisher solutions, thus improving the compactness of required materials. At the same time, the long term stability of the materials must be maintained.
For the developer processing step, sets of multiple liquid concentrates are used to prepare the developer replenisher and working strength developer by mixing the liquid concentrates and diluting them with water. This process has found wide-reaching commercial success within the photographic processing industry. A majority of the commercially available photographic processing equipment is based on this system.
In the case of color developers, multiple liquid concentrate parts are necessary due to chemical reactions that occur between hydroxyl amine (HA) and derivatives thereof and p-phenylenediamine and derivatives and salts thereof and the sulfite preservative commonly used when stored together in liquid form. If these chemicals are incorporated into a concentrated solution, the chemical reaction between them proceeds rapidly, severely shortening the shelf life of the composition. Thus, a single concentrated solution that has hydroxyl amine, sulfite preservative and p-phenylenediamine heretofore has not been possible.
In an effort to reduce the number of parts of the developer concentrate, the industry has investigated the use of alternative developer forms and formulations. For example, Abe (U.S. Pat. No. 5,837,435) teaches the use of limited hydroxylamine derivatives in a concentrated solution. However, photographic performance with these derivatives on certain films can produce variations when compared to using hydroxylamine sulfate. In addition, Abe is limited in specific gravity range, thereby not providing compact concentrates.
Kleinschmidt, DE 3106775, discloses a single-part liquid color photographic developer concentrate. However, this developer concentrate requires organic solvents for dissolution to form a replenisher or working developer solution. These solvents also can produce variations on certain films.
Ishida and Koboshi (U.S. Pat. No. 5,480,768) propose the use of solid tablets of chemicals to prevent the chemical interactions that occur in liquid concentrates. Preferably, each chemical should be in the form of a tablet, necessitating the dissolution of multiple tablets to form a developer solution. Using solid tablets of chemicals results in a low dissolution speed of the chemicals in the replenisher or working strength developer. Thus, it is necessary to use water warmed up to around 40xc2x0 C. to speed dissolution. Warm water-supplying equipment and agitation equipment are required, making solid tablets very difficult to handle in small-scale processing stores (mini- or micro-laboratories). Thus, the solid tablets are disadvantageous because they require special handling and mixing equipment not common in the photographic industry, as opposed to existing processors that allow pourable concentrates to be mixed with water. Because of these disadvantages, the use of tablets has not become widespread within the photographic industry.
Yamashita and Ueda (EP 640,872) also teach a solid photoprocessing composition in the form of a coated tablet. The tablet is coated with one or more of polyalkylene glycol, mono- and di-saccharides or vinyl polymer having a betaine structure to resist abrasion and deterioration. Due to the slow dissolution speed of the tablet coating, the tablets must be added directly to the working solution, again requiring special handling and mixing equipment. In addition, there are many photographic processing chemical components known in the art that are available only as liquids that are excluded from use by this method.
There is a continuing need in the industry to produce a more compact, color developer concentrate that is stable, pourable, easily dissolved, readily mixed in existing photographic processing equipment to prepare both replenisher and working strength developer solutions, and has improved photographic performance and environmental impact, such as using less packaging material thereby reducing the discharge of waste to the environment.
The present invention provides a stable, pourable photographic developer concentrate composition comprising a concentrate and a solid component. The developer concentrate composition can be used in existing mixing and processing equipment without modification. Further, the developer concentrate composition, concentrate and solid can be formulated using existing and readily available chemicals necessary for photographic processing.
The present invention further provides a single developer concentrate composition in which a concentrate and a solid co-exist or are in contact with each other within the same container. The solid is coated with, or encapsulated in, a material that is insoluble in the concentrate of the developer concentrate composition but is readily and completely soluble when the developer concentrate composition is diluted with water to prepare a replenisher or working strength developer. The developer concentrate composition has excellent storage stability even for extended periods of time at high temperature because chemical components known to react with each other in liquid form are present within the same container without reacting.
In a preferred embodiment, the invention comprises a color developer concentrate composition of a concentrate comprising water and at least one color developer chemical component and a solid comprising at least one color developer chemical component, wherein the solid is isolated from the concentrate by a coating insoluble in the concentrate but readily soluble when diluted with water to prepare a replenisher or working strength developer. Preferably, the concentrate and solid are present in one container. More preferably, the coating comprises an alkali metal sulfate.
In preferred embodiments, the concentrate comprises one or more of a color developer chemical selected from hydroxylamine or a derivative thereof, p-phenylenediamine or a derivative or salt thereof and sulfite. Preferably, the color developer chemical is one or more of a hydroxylamine derivative and sulfite.
In other preferred embodiments, the solid comprises one or more of a color developer chemical selected from hydroxylamine or a derivative thereof, p-phenylenediamine or a derivative or salt thereof and sulfite. Preferably, the color developer chemical is one or more of hydroxylamine or a derivative thereof, more preferably hydroxylamine sulfate, and p-phenylenediamine or a derivative or salt thereof.
In another embodiment, a solid comprises a color developer chemical component comprising at least one color developer chemical suitable for developing silver halide photosensitive materials, and a coating, wherein the coating is insoluble in the concentrate of the developer concentrate composition and is soluble when dissolved with water to prepare a replenisher or working strength developer. In a preferred embodiment, the coating comprises an alkali metal sulfate.
In another embodiment, the solid comprising at least one color developer chemical component is enclosed in a coated tablet or capsule wherein the coating comprises one or more of (a), (b), (c) or (d) as follows:
a. an alkali metal sulfate
b. a polyalkylene glycol having a weight average molecular weight of 1,000 to 20,000;
c. a polyethylene oxide having a weight average molecular weight of 100,000 to 750,000; and
d. a cellulosic polymer having a weight average molecular weight of 10,000 to 1,000,000.
In a preferred embodiment, the solid comprising at least one color developer chemical component is enclosed in a coated tablet or capsule wherein the coating comprises an alkali metal sulfate and one or more of (a), (b) or (c) as follows:
a. a polyalkylene glycol having a weight average molecular weight of 1,000 to 20,000;
b. a polyethylene oxide having a weight average molecular weight of 100,000 to 750,000; and
c. a cellulosic polymer having a weight average molecular weight of 10,000 to 1,000,000.
The invention is further directed to a replenisher and working strength developer made from dilution of the developer concentrate composition in water. A method of processing exposed photosensitive material with the working strength developer is also described.
These and other preferred embodiments are described in detail below.
The color developer concentrate composition of the present invention has a concentrate and a solid component stored in one container such that the concentrate and solid component do not react. The developer concentrate composition is used to form a replenisher or working strength developer by undergoing dilution with water. The developer concentrate composition does not require admixture with any other chemicals in order to form a replenisher or working strength developer.
The concentrate is a solution of water and at least one color developer chemical useful in developing silver halide photographic materials. Herein, xe2x80x9csolutionxe2x80x9d is defined to mean a mixture of two or more ingredients, one of which is water, to form a homogenous liquid. Thus, the concentrate can include a suspension of solids within water or a colloidal mixture.
The concentrate has at least one color developer chemical dissolved or suspended therein. The total amount of color developer chemical present is in an amount of at least about 25% (w/w) by weight of the concentrate, preferably at least about 35% (w/w), more preferably between about 40%(w/w) and about 60% (w/w), and most preferably between about 44% (w/w) and about 52% (w/w). The color developer chemical preferably includes one or more of hydroxylamine or a derivative thereof, p-phenylenediamine or a derivative or salt thereof and a sulfite. If both sulfite and a hydroxylamine derivative are present in the concentrate, the hydroxylamine derivative will be in a form that is stable in the presence of sulfite, such as a long-chain derivative of hydroxylamine. Such derivatives of hydroxylamine that are stable in the presence of sulfite are known to practitioners in the art. Most preferably, the concentrate includes one or more of a sulfite and p-phenylenediamine or a derivative or salt thereof. The concentrate also can contain other suitable color developer chemicals as known to practitioners in the art. The concentrate is formed by any means known to practitioners in the art.
The solid component comprises at least one color developer chemical useful in developing silver halide photographic materials. Preferably, the solid compound of the color developer concentrate composition comprises one or more of hydroxylamine or a derivative thereof, p-phenylenediamine or a derivative or salt thereof and a sulfite. More preferably, the solid comprises one or more of hydroxylamine sulfate and p-phenylenediamine or a derivative or salt thereof. Each of hydroxylamine or a derivative thereof, p-phenylenediamine or a derivative or salt thereof and a sulfite can be present in solution, in the solid, or in both.
Both hydroxylamine or a derivative thereof and sulfite can be present in the solid component. In the concentrate, if both hydroxylamine or a derivative thereof and sulfite are present, the hydroxylamine or derivative thereof must be in a form that is stable in the presence of sulfite, such as a long-chain derivative of hydroxylamine. Such derivatives of hydroxylamine that are stable in the presence of sulfite are known to practitioners in the art.
When the solid component includes hydroxylamine or a derivative thereof, preferably hydroxylamine sulfate, it is in an amount of at least about 30% (w/w) by weight of the solid, preferably at least about 50% (w/w). When the solid includes p-phenylenediamine or a derivative or salt thereof, it is in an amount of at least about 40% (w/w) by weight of the solid, preferably at least about 60% (w/w). When the solid includes more than one of hydroxylamine or a derivative thereof, p-phenylenediamine or a derivative or salt thereof or sulfite, the combined amount is at least about 70% (w/w) by weight of the solid, preferably at least about 85% (w/w). The solid can optionally include other suitable color developer chemicals useful in developing silver halide photographic materials as known to practitioners in the art.
The solid can contain multiple color developer solid chemicals of various particle sizes, including powders, granules and crystals. The solid chemicals are formed into a tablet, encapsulated, or otherwise made into a suitable solid form as known to practitioner in the art by any means known to practitioners in the art. Preferably, a tablet is formed by compression molding the solid color developer chemicals of the solid component. The solid may contain a binding agent as known to practitioners in the art, such as but not limited to polyethylene glycol, to aid in the formation of a tablet or other suitable solid form of the color developer solid chemicals.
A preferable tablet-making process is to form a tablet after granulating the solid color developer chemicals of the solid component. As compared to a solid composition prepared simply by mixing the chemicals to form a tablet, there is an advantage that improved solubility and storage stability are achieved by first granulating the solid color developer chemicals.
Any conventionally known granulation process can be carried out prior to the tablet-making process. The granulation process can be selected from fluidized-bed granulation process, extrusion granulation process, compression granulation process, crush granulation method, fluid-layer granulation process, spray-dry granulation process, or any other granulation process known to practitioners in the art.
Any conventional compression molding machine, such as a single-engined compression molding machine, a rotary-type compression molding machine, a briquetting machine, or the like as known to practitioners in the art can be used to form a tablet. The tablet can be formed in any desirable shape and size, and preferably is suitable for use with existing color photographic development equipment. Preferably, the tablet has a thickness in the range of from about 2 mm to about 8 mm, and a diameter of from about 5 mm to about 15 mm, although smaller or larger tablets can be formed as desired.
A tensile strength of the tablet of about 5 to 50 kg/cm2 is desirable from the viewpoint of manufacturing operation and physical distribution thereof, although tensile strengths outside this range can be used as known to practitioners in the art. If the tensile strength is at least 5 kg/cm2, there are few occurrences of cracking or breaking-off of the tablet during coating as described elsewhere herein.
The solid component is coated with (if in tablet form) or encapsulated in a layer that is insoluble in the concentrate but soluble when diluted with water to form a replenisher or working strength developer. The coating of the solid component may include one or more of an alkali metal sulfate, a polyalkylene glycol having a weight average molecular weight of from about 1,000 to about 20,000, a polyethylene oxide having a weight average molecular weight of from about 100,000 to about 750,000, or a cellulosic polymer having a weight average molecular weight of from about 10,000 to about 1,000,000.
The coating is applied to the solid component in an amount of about 1% (w/w) dry weight to about 50% (w/w) dry weight by weight of the solid component. Preferably, the coating is applied in an amount of about 5% (w/w) dry weight to about 30% (w/w) dry weight by weight of the solid component.
The coating can consist of one or more layers which can be of the same or a different composition, provided at least one layer is insoluble in the concentrate but soluble when diluted with water to form a replenisher or working strength developer. At least one layer of the coating may comprise one or more of an alkali metal sulfate, a polyalkylene glycol having a weight average molecular weight of from about 1,000 to about 20,000, a polyethylene oxide having a weight average molecular weight of from about 100,000 to about 750,000, and a cellulosic polymer having a weight average molecular weight of from about 10,000 to about 1,000,000. In preferred embodiments, at least one layer of the coating contains an alkali metal sulfate.
As used herein, alkali metal sulfates may include any one or more alkali metal sulfate as known to practitioners in the art. Examples of such alkali metal sulfates include, but are not limited to, potassium sulfate, sodium sulfate, and combinations thereof.
Polyalkylene glycols having a weight average molecular weight of from about 1,000 to about 20,000 as used herein include any one or more polyalkylene glycol having a weight average molecular weight of from about 1,000 to about 20,000 known to practitioners in the art. Suitable examples of such polyalkylene glycols include, but are not limited to, Carbowax(copyright) PEG (polyethylene glycol) 1450, Carbowax(copyright) PEG 4000, Carbowax(copyright) PEG 8000, and combinations thereof.
Polyethylene oxides having a weight average molecular weight of from about 100,000 to about 750,000 include any one or more polyethylene oxide (PEO) having a weight average molecular weight of from about 100,000 to about 750,000 known to practitioners in the art. Suitable examples of such polyethylene oxides include, but are not limited to, PEO 100,000, PEO 200,000, PEO 750,000, sulfonated polystyrene 200,000, polyacrylic acid 500.000, and combinations thereof.
Cellulosic polymers having a weight average molecular weight of from about 10,000 to about 1,000,000 include any one or more cellulosic polymer having a weight average molecular weight of from about 10,000 to about 1,000,000 as known to practitioners in the art. Suitable examples of such cellulosic polymers include, but are not limited to, methyl cellulose, hydroxy ethyl cellulose, hydroxypropyl methyl cellulose, and combinations thereof.
One or more alkali metal sulfate can be present in the coating in an amount of from about 1% (w/w) dry weight to about 50% (w/w) dry weight by weight of the solid component, preferably in an amount of from about 5% (w/w) to about 30% (w/w), more preferably in an amount of from about 10% (w/w) to about 25% (w/w), and most preferably in an amount of from about 10% (w/w) to about 20% (w/w). Preferably, the alkali metal sulfate is sodium sulfate, potassium sulfate, or a combination thereof. One or more of a polyalkylene glycol, a polyethylene oxide or a cellulosic polymer as described herein can be present in the coating in an amount of from about 1% (w/w) dry weight to about 8% (w/w) dry weight by weight of the solid component, preferably in an amount of about 1% (w/w) to about 5% (w/w). Preferably, a cellulosic polymer is present in an amount of from about 1% (w/w) dry weight to about 5% (w/w) dry weight by weight of the solid component. The combined weight of all coating layers should not exceed 50% (w/w) dry weight by weight of the solid component, preferably 30% (w/w) dry weight by weight of the solid component.
In the present invention, exemplary methods for coating the solid component in tablet form are given below. Other methods of coating the tablet as recognized by practitioners in the art can also be used. Preferable methods of coating the tablet include: dipping the tablet into the coating material made liquid by heating or dissolving in a solvent; coating the tablet with the coating material made liquid by dissolving in a solvent or heating; and spraying the coating made liquid by dissolving in a solvent or heating onto the surface of the tablet.
Coating by a continuous process such as spraying followed by drying is preferable in order to increase production speed at manufacture of the solid component. Spraying or pan coating are preferable methods of coating when multiple layers of coating are to be used.
Alternately, the solid component can be encapsulated by the coating material as described herein by any suitable method as known to practitioners in the art.
Suitable derivatives and salts of p-phenylenediamine for use in the invention include:
4-amino-3-methyl-N-ethyl-N-(xcex2-(methanesulfonamido)ethyl)aniline,
N,N-diethyl-p-phenylenediamine,
N,N-diethyl-p-phenylenediamine monohydrochloride,
N,N-diethyl-p-phenylenediamine sulfur dioxide complex,
N,N-diethyl-p-phenylenediamine sulfate,
2-amino-5-diethylamino-toluene,
4-amino-N-ethyl-N-(xcex1-methanesulphonamidoethyl)-m-toluidine,
4-amino-N-ethyl-N-(xcex2-methanesulphonamidoethyl)-m-toluidine sesquisulfate monohydrate,
4-amino-3-methyl-N-ethyl-N-(xcex1-hydroxy-ethyl)-aniline,
4-amino-3-(xcex1-methylsulfonamidoethyl)-N,N-diethylaniline,
4-amino-N,N-diethyl-3-(Nxe2x80x2-methyl-xcex1-methylsulfonamido)-aniline,
N-ethyl-N-methoxy-ethyl-3-methyl-p-phenylenediamine,
N-ethyl-N-(xcex2-hydroxyethyl)-p-phenylenediamine sulfate,
4-amino-3-methyl-N,N-diethylaniline,
4-amino-3-methyl-N-ethyl-N-(3-hydroxypropyl)aniline,
4-amino-N-ethyl-N-(2-hydroxyethyl)aniline,
4-amino-3-methyl-N-ethyl-N-(2-hydroxyethyl)aniline,
4-amino-3-methyl-N-ethyl-N-(2-hydroxyethyl)aniline sulfate,
4-amino-3-methyl-N-ethyl-N-(2-methanesulfonamidoethyl)aniline,
2-amino-5-diethylaminotoluene hydrochloride,
N-(2-amino-5-N,N-diethylaminophenylethyl)methanesulfonamide,
N,N-dimethyl-p-phenylenediamine,
4-amino-3-methyl-N-ethyl-N-(2-methoxyethyl)aniline,
4-amino-3-methyl-N-ethyl-N-(4-hydroxybutyl)aniline,
4-amino-3-methyl-N-ethyl-N-(2-butoxyethyl)aniline,
4-amino-N-ethyl-N-(2-methoxyethyl)-m-toluidine di-p-toluene sulfonate,
and the like, and salts thereof. Other suitable salts and derivatives of p-phenylenediamine are known to practitioners in the art.
Other color developing chemicals as known to practitioners in the art can be included in either the concentrate or the solid. These can include, but are not limited to, for example, buffering agents, antioxidants, chelating agents, antifoggants, development accelerators or restrainers, surfactants, and the like.
One or more buffering agents as known to practitioners in the art can be present in one or more of the concentrate or solid in order to maintain the pH of the replenisher and working strength developer upon dilution of the developer concentrate composition in water. Suitable pH control agents include, but are not limited to, inorganic alkali metal hydroxides, alkali metal carbonates, and the like. In the art, useful alkali metal hydroxides include lithium, sodium and potassium hydroxide. Useful alkali metal carbonates include lithium, sodium and potassium carbonates. The buffering agent may be present in an amount up to about 33% (w/w) of the concentrate weight, or in an amount of less than about 10% (w/w) of the solid weight. If present in both, the total amount of buffering agent does not exceed about 36% of the total weight of the concentrate and solid. Practitioners in the art will recognize that other suitable amounts outside these ranges may also be used.
One or more inorganic or organic antioxidants as known to practitioners in the art can be added to the concentrate or solid as a preservative to protect the color developing agent. These compounds are preferably added to the concentrate in an amount of about 2% to about 7% of the concentrate weight, or to the solid in an amount of less than about 10% of the solid weight. The total amount of antioxidants in the developing concentrate composition does not exceed about 7% of the total weight of the concentrate and solid, although other suitable amounts outside these ranges can be used as recognized by practitioners in the art.
Various chelating agents as known to practitioners in the art can be present in one or more of the concentrate or solid component of the color developer concentrate composition as precipitation inhibitors of calcium or magnesium in the replenisher or working strength developer, or as stability improving agents of the developer concentrate composition. Examples of suitable chelating agents include, but are not limited to, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, N,N,N-trimethylenephosphonic acid, ethylenediamine-N,N,Nxe2x80x2,Nxe2x80x2-tetramethylenesulfonic acid, transcyclohexanediaminetetraacetic acid, 1,2-diaminopropanetetraacetic acid, glycol ether diaminetetraacetic acid, ethylenediamine-o-hydroxyphenylacetic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, N,Nxe2x80x2-bis(2-hydroxybenzyl)ethylenediamine-N,Nxe2x80x2-diacetic acid and 1,2-dihydroxybenzene-4,6-disulfonic acid. Chelating agents may be used in combinations of two or more, if desired. The amount of the chelating agent in the color developer concentrate composition should be sufficient to sequester Group II and transition metal ions present in the dilution water used to prepare the replenisher or working strength developer.
Other additives such as antifoggants, alkanolamines, development accelerators, development restrainers, wetting agents, fragrances and surfactants, for example, as known to practitioners in the art, can optionally be included in one or more of the concentrate or solid. Amounts of each additive suitable for use in the concentrate and/or solid of the invention are readily determinable by practitioners in the art.
The silver halide color photosensitive material to which the present invention is applicable is a photosensitive material which can be processed with a color developer containing a sulfite. Specific examples of such materials include silver chlorobromide emulsion- or silver bromide emulsion-coated color papers and color auto positive papers, and silver iodobromide emulsion-coated color negative films, color reversal films and color reversal papers. Of these materials, color negative films are preferred for use with the present invention.
The concentrate and solid of the invention are desirably enclosed in a single container or package such that the concentrate is in contact with the solid and opening or rupturing of the container causes both the concentrate and solid to be exposed or released. The concentrate and solid forming the color developer concentrate composition are contained by any suitable means known in the art for wrapping or packaging of developer concentrate compositions, including, but not limited to, packages of film, plastic, coated paper, aluminum, or any combination thereof. Preferably, the developer concentrate composition is packaged in a manner suitable for use with existing color photographic developing equipment, in particular, with automatic feeding equipment used in color photographic processing systems.
A method for processing an image-wise exposed photographic color silver halide emulsion using the developer concentrate composition disclosed herein includes mixing the developer concentrate composition with water to form a working strength developer, and processing the exposed photosensitive material with the working strength developer. While the processing parameters are known to practitioners in the art, preferably the process is carried out for about 20 seconds to about 4 minutes at a temperature of from about 30-50xc2x0 C. Other suitable processing methods and parameters which may be used with the developer concentrate composition described herein will be apparent to practitioners in the art.
Use of the above process with the developer concentrate composition of the invention for developing image-wise exposed photographic color silver halide emulsions avoids the possibility of mixing errors inherent in using conventional sets of multiple liquid concentrates which must be mixed in a specific addition order prior to use. In the process of the invention, the developer concentrate composition may be either manually added by pouring into the replenisher tank containing dilution water at prescribed intervals, or it can be metered into the replenisher tank with water based on the actual quantity of photographic material processed, or based on some measured property of the process bath such as, for example, the specific gravity or pH of the working strength developer, the concentration of depleted components therein as determined by chemical analysis, the accumulation of decomposition products, the accumulation of extracts from the photographic material, other properties known to practitioners in the art, or any combination of the foregoing.
To form a replenisher, the color developer concentrate composition described herein is diluted with water such that the developer concentrate composition is present in water in an amount up to about 8% (w/w), preferably in an amount of from about 4.5% to about 7.5%. To form a working strength developer, the color developer concentrate composition described herein is diluted with water such that the developer concentrate composition is present in water in an amount up to about 8% (w/w), preferably in an amount of from about 2.0% to about 7.5%.
Multiple solid components can be used within the developer concentrate composition used to form a replenisher or working strength developer. When multiple solid components are used, each solid component can have the same or a different chemical composition.
The use of solid components having different chemical compositions in a single concentrate allows various chemicals known to react when stored together to be stored in a single package over long periods of time without reacting. Thus, hydroxylamine or derivatives thereof, p-phenylenediamine or derivatives or salts thereof and sulfite may be stored in a single container or package, but each contained in a different solid component such that they do not react during storage. This minimizes the number of containers required for handling, eases addition of chemicals for forming replenishers or working strength developers because only one container or package of chemicals is needed, and greatly improves the shelf life of the developer chemicals.